Liquid crystal display

ABSTRACT

The present invention relates to a liquid crystal display provided with an electrostatic protection element and an object of the present invention is to provide the liquid crystal display provided with superior redundancy and at the same time a sufficient protection function against static electricity in which relatively low voltage generates for a long period of time. Electrostatic protection element sections  28  and  30  are provided with a first TFT  32  having a source electrode (S) and a drain electrode (D) where the source electrode (S) is connected to external output electrodes  16  and  18  and the drain electrode (D) is connected to common wirings  22  and  24,  a second TFT  38  having a conductor  42,  a source electrode (S), a drain electrode (D) and a gate electrode (G) where the conductor  42  is connected to the gate electrode (G) of the first TFT  32,  the source electrode (S) is connected to the external output electrodes  16  and  18,  the drain electrode (D) is connected to the conductor  42  and the gate electrode (G) is electrically floated, and a third TFT  40  having a source electrode (S), a drain electrode (D) and a gate electrode (G) where the source electrode (S) is connected to the common wirings  22  and  24,  the drain electrode (D) is connected to the conductor  42  and the gate electrode is electrically floated.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention related to an active matrix type liquidcrystal display provided with a thin film transistor (hereinafter,referred to as TFT) as a switching element, and specifically relates tothe liquid crystal display provided with an electrostatic protectionelement protecting the TFT formed on a substrate on an array side andareas between bus lines from a destruction or a shortage due to staticelectricity.

[0003] 2. Description of the Related Art

[0004] The active matrix type LCD is widely used in computers orequipment for the use of OA (Office Automation) as a flat panel displayproviding superior picture quality. In this active matrix type LCD, avoltage is applied electrode from both electrodes to a liquid crystallayer sealed between the substrate on the array side forming TFT andpixel electrode and an opposing substrate forming common, therebydriving liquid crystal.

[0005] A plurality of gate bus lines to which a scanning signal issequentially input to select a driving display pixel are formed inparallel to each other on the substrate on the array side. Further, aninsulation film is formed on the plurality of gate bus lines, and aplurality of data bus lines in substantially orthogonal to the gate buslines are formed on an insulation film. Each area decided by theplurality of gate bus lines and the plurality of data bus lines formedin orthogonal to each other in a matrix shape becomes a pixel area, andthe TFT and the display electrode are formed in each pixel area. A gateelectrode of the TFT is connected to a predetermined gate bus line, adrain electrode is connected to a predetermined data bus line, and asource electrode is connected to the display electrode in the pixelarea.

[0006] Incidentally, since the TFT for controlling the operation ofliquid crystal of the TFT-LCD, gate bus lines, data bus lines and thelike are formed on the glass substrate which is an insulation material,the TFT, gate bus lines, data bus lines and the like are basically weakagainst static electricity. Therefore, if static electricity isgenerated on the substrate on the array side during a period from thesubstrate process on the array side constructing the TFT to the panelprocess sealing liquid crystal by attaching the substrate on the arrayside and the opposing substrate and mounting a driver IC and the like,defects such as a destruction of the TFT, a change in characteristics ofthe TFT, a shortage between each of the bus lines are generated, therebyresulting in a considerable reduction in fabrication yield of panels.Thus, a reliable measure to protect the elements and the bus lines onthe substrate on the array side from static electricity is required.

[0007] As a measure to protect the substrate on the array side fromstatic electricity, for example, a method connecting all the bus linesto a common electrode (short ring) to keep the same potential is known.The short ring is formed by materials for the data bus lines or the gatebus lines when the data bus lines or the gate bus lines are formed.Thus, each bus line is electrically connected with the value ofresistance less than several kΩ. Therefore, even if a specific area onthe panel is charged with electricity, the electric charges areinstantly dispersed, thereby preventing the TFT in a display from adevice destruction or a change in characteristics.

[0008] However, according to this method, since each bus line isshort-circuited to each other, an independent signal can not be appliedto each bus line. Therefore, a problem occurs, in which an arrayinspection (a TFT inspection) performing a characteristic test of theTFT of each pixel by detecting the amount of electric charges when theelectric charges are kept between the pixel electrode and the commonelectrode in the display panel can not be performed. Further, since theshort ring electrically connects the adjacent bus lines at lowresistance, the short ring is required to be removed either in the panelprocess or in the unit assembling process after the panel is completed.Thus, a problem exists in which a measure against static electricity isnot taken in the processes after the unit assembling process.

[0009] Accordingly, a method of arranging a resistive component betweenthe short ring and each bus line is conceived. FIG. 28 is a diagramdescribing the conventional technology connecting the resistivecomponent between the bus line and the short ring, which is disclosed inthe publication of Japanese Laid Open Patent Application No. 8-101397.FIG. 28 shows a part of a substrate surface on the array side and aresistance layer 400 is formed by patterning an ITO (indium tin oxide)formed on a gate metal or on a drain metal into a zigzag line at the endportion of a bus line 504. A tip of the zigzag-shape resistance layer400 is connected to a short ring 506. The array inspection is possibleaccording to this structure. Normally, this resistance layer 400 and theshort ring 506 are removed by disconnecting a scribe line SL shown bythe dotted line in the diagram in the panel scribe process whenassembling the panel.

[0010] However, according to this method, in order to obtain a higherresistance using ITO, an area is required to secure to lengthen thedistance of the zigzag-shape. Thus, a problem that an external size ofthe panel becomes large exists.

[0011] Besides the methods described above, a method for inserting anelectrostatic protection element such as a transistor and the likebetween the bus line and the short ring is conceived. For example, inthe publication of Japanese Laid Open Patent Application No. 61-79259, amethod of connecting the gate electrode and the source/drain electrodeby a capacitive coupling is shown.

[0012]FIGS. 29a and 29 b are diagrams describing the conventionaltechnology shown in the publication of Japanese Laid Open PatentApplication No. 61-79259. FIG. 29a shows a state of a part of thesubstrate on the array side when viewing toward the substrate and FIG.29b shows a cross section of the electrostatic protection element. Asshown in FIG. 29a, an electrostatic protection element 500 has a TFTstructure arranged between an external output electrode 504 at the endportion of a bus line 502 and the short ring 506. The electrostaticprotection element 500 is formed by the same process as the TFT formedin the pixel area on a glass substrate 508. As shown in FIG. 29b, a gateelectrode 510 is formed on the glass substrate 508 and an operatingsemiconductor layer 514 composed of, for example, amorphous silicon(hereinafter, abbreviated as a-Si) is formed on the gate electrode 510via a gate insulation film 512. A protection film 520 is formed on theoperating semiconductor layer 514 and a source electrode 518 and a drainelectrode 516 are formed on both sides of the operating semiconductorlayer 514 sandwiching the protection film. The drain electrode 516 isconnected to the short ring 506 and the source electrode 518 isconnected to the external output electrode 504. When viewing to thedirection of the substrate surface, the gate electrode 510 has a planeoverlapping with the source/drain electrodes 518 and 516 and isconnected with the source/drain electrodes 518 and 516 by capacitivecoupling. Therefore, when high voltage is generated due to staticelectricity between the source/drain electrodes 518 and 516, since thepotential of the gate electrode 510 becomes the middle of the potentialdifference generated between the source/drain electrodes 518 and 516, achannel is created at the operating semiconductor layer 514, therebyreleasing the electric load due to static electricity from the bus line502.

[0013] However, since the structure of this electrostatic protectionelement 500 has a single structuring element, the redundancy is poor. Inother words, since high voltage due to static electricity is received byonly one TFT, the electrostatic protection element 500 is easilydestroyed and when the area between the bus line 502 and the short ring506 is insulated due to the destruction, the possibility of the TFT inthe pixel area to be exposed to static electricity increases. Further,even if irregularities due to static electricity do not occur, if theelectrostatic protection element 500 is short-circuited due to somereason, a TFT test can not be performed.

[0014] Next, the electrostatic protection circuit having more redundancythan the structure shown in FIGS. 29a and 29 b which is disclosed in thepublication of Japanese Laid Open Patent Application No.10-303431 isdescribed with reference to FIG. 30. The source electrode (S) of thefirst TFT 530 which is the electrostatic protection element is connectedto an external output electrode 502 of the bus line, and the drainelectrode (D) on the other side is connected to the short ring 506. Thegate electrode (G) of the first TFT 530 is connected to a conductor 536which is electrically floated from both the external output electrode502 and the short ring 506. On the other hand, the source electrode (S)and the gate electrode (G) of the second TFT 532 are connected to theexternal output electrode 502 of the bus line and the drain electrode(D) on the other side is connected to the conductor 536. Further, thedrain electrode (D) of the third TFT 534 is connected to the conductor536 and the source electrode (S) and the gate electrode (G) on the otherside are connected to the short ring 506. When positive high voltage isgenerated in the bus line with respect to the short ring 506 due tostatic electricity, high voltage is applied to the gate electrode (G) ofthe second TFT 532 and a channel is formed, thereby rapidly increasingthe conductivity. On the other hand, since the gate electrode (G) of thethird TFT 534 is connected to the short ring 506, a channel is notformed and the conductivity remains to be very small. This difference inconductivity is very large, and in consequence, the potential of theconductor 536 is substantially equal to the potential of the bus line.As a result, a channel is formed by applying the voltage between the busline and the short ring 506 at the gate electrode of the first TFT 530which is the electrostatic protection element and the electric chargecan be released. It will be noted that the second and the third TFT's532 and 534 do not basically run the current and are used only tocontrol the gate potential of the first TFT 530.

[0015] In this manner, in the above electrostatic protection circuit,since the gate electrodes of the second and the third TFT's 532 and 534are connected to the external output electrode 502 of the bus line orthe short ring 506, the potential difference between the external outputelectrode 502 and the short ring 506 is instantly liquidated. However,when the voltage generated by static electricity reduces as the timepasses, the potential of the conductor 536 also reduces and theconductivity of the first TFT 530 reduces. Thus, when the voltage isrelatively low (˜ several volts) due to static electricity, theefficiency of releasing the electric charges is reduced.

[0016] Also, based on the previous fabrication experiences, obstaclesdue to static electricity are known to be occurred by sharp pulse-likestatic electricity at extremely high voltage for a short period of timeand static electricity continuously applied to each element for a longperiod of time even if the voltage is relatively low. Therefore,although the electrostatic protection circuit described in thepublication of Japanese Laid Open Patent Application No. 10-303431 canbe expected to be effective in the former case, little result isexpected in the latter case as the path for the current to escape is cutoff when the voltage is reduced to a certain extent. Further, accordingto the electrostatic protection circuit described in the abovepublication, since the current due to static electricity all flows inthe first TFT, the redundancy is poor and the load is exceedinglyincreased, therefore the possibility of the first TFT to be destroyedexists. Furthermore, since the gate electrode (G) of the second TFT 532is directly connected with the external output electrode 502 of the busline and the gate electrode (G) of the third TFT 534 is directlyconnected with the short ring 506, the redundancy against shortage isreduced.

[0017] As still another conventional electrostatic protection circuit,there is a structure shown in FIG. 31, which is described in thepublication of Japanese Laid Open Patent Application No. 7-60875. Thisis an electrostatic protection circuit connecting between the bus line504 and the short ring 506 via a resistive component by a two-waytransistor using non-linear elements 402 and 404. Besides the two-waytransistor, a non-linear element such as a shot-key diode, which can bea resistive component, may be also used. Since the resistive componentby the non-linear element has a sufficient high resistive component soas not to affect the operation of each bus line, the resistive componentby the non-linear element can be remained after the panel is completed.Further, as to static electricity, since some current which can disperseelectric charges flows, the resistive component by the non-linearelement functions as an anti-electrostatic element.

[0018] Although in the method arranging the high resistive component bythe non-linear element such as the two-way transistor, the highresistive component can be formed in a relatively small area, problemsoccur with respect to controlling the current since the structure of thedevice becomes complex and moreover the resistive component is alteredby an external charges (for example, static electricity) owing to thenon-linear element. Further, since the high resistive component can notbe formed outside the ensured area for operation of operatingsemiconductor film of the transistor such as the area adjacent to an endface of glass, a problem of not being able to make the size of the panellarge against a mother glass exists.

[0019] Accordingly, although the short ring is required to be removed inthe panel process or in the unit assembly process after the panel iscompleted according to the conventional liquid crystal display, aproblem exists in which a measure against static electricity can not betaken in the processes after the short ring is removed.

[0020] Further, in the method arranging the zigzag pattern using theITO, a problem exists in which if the length of the zigzag pattern islong, the external size of the panel becomes large.

[0021] Furthermore, the conventional liquid crystal display has problemsin which the electrostatic protection element (circuit) for preventing adevice destruction due to static electricity is poor in redundancy, thearea between the bus line and the short ring is easily short-circuitedor the electrostatic protection element does not function as aprotection circuit against the static electricity generating relativelylow voltage for a long period of time.

[0022] Also, if the non-linear element such as the two-way transistor isused as the high resistive component, the structure of the devicebecomes complex and the aspect of controlling the current isdisadvantageous as well. Further, since the non-linear element can notbe formed adjacent to the end face of the glass, a problem of not beingable to make the size of the panel large against the mother glassexists.

SUMMARY OF THE INVENTION

[0023] An object of the present invention is to provide a liquid crystaldisplay provided with an electrostatic protection circuit superior inredundancy.

[0024] Another object of the present invention is to provide a liquidcrystal display provided with a sufficient protection function againststatic electricity generating relatively low voltage for a long periodof time.

[0025] Further object of the present invention is to provide a liquidcrystal display in which measures for static electricity can be takenuntil the last stage of the substrate assembly process.

[0026] Furthermore object of the present invention is to provide aliquid crystal display in which an electrostatic protection elementsection does not affect the size of a panel.

[0027] Another object of the present invention is to provide a liquidcrystal display having the electrostatic protection element sectionwhich is simple in structure of the device and not disadvantageous in anaspect of controlling the current.

[0028] Above objects are achieved by an active matrix type liquidcrystal display comprising a switching element formed for each of aplurality of pixels decided by a plurality of bus lines and a short ringconnected to the plurality of bus lines, and an electrostatic protectionelement portion formed between each of the plurality of bus lines andthe short ring, wherein the electrostatic protection element portioncomprises a thin film transistor having a source or a drain electrodeconnected to the bus line and the drain or the source electrodeconnected to the short ring, a first resistor connecting a gateelectrode of the thin film transistor to the bus line, and a secondresistor connecting the gate electrode of the thin film transistor tothe short ring.

[0029] In the liquid crystal display described above, the secondresistor may be a common resistor connecting the gate electrodes of theplurality of thin film transistor to the short ring.

[0030] Further, the above object are achieved by an active matrix typeliquid crystal display comprising a switching element formed for each ofa plurality of pixels decided by a plurality of bus lines and anelectrostatic protection element portion formed between the adjacent buslines, wherein the electrostatic protection element portion comprises athin film transistor having a source or a drain electrode connected toone of the adjacent bus lines and the drain or the source electrodeconnected to the other of the bus lines, a first resistor connecting agate electrode of the thin film transistor to one of the bus lines, anda second resistor connecting the gate electrode of the thin filmtransistor to the other of the bus lines.

[0031] Furthermore, above objects are achieved by an active matrix typeliquid crystal display comprising a switching element formed for each ofa plurality of pixels decided by a plurality of bus lines, a short ringconnected to the plurality of bus lines, and

[0032] a electrostatic protection element portion formed between each ofthe plurality of bus lines and the short ring, wherein the electrostaticprotection element portion comprises a first thin film transistor havinga source or a drain electrode connected to the bus line and the drain orthe source electrode connected to the short ring, a conductive materialconnected to a gate electrode of the first thin film transistor, asecond thin film transistor having a source or a drain electrodeconnected to the bus line, the drain or a source electrode connected tothe conductive material, and a gate electrode electrically floated, anda third thin film transistor having a source or a drain electrodeconnected to the short ring, the drain or the source electrode connectedto the conductive material, and a gate electrode electrically floated.

[0033] In the liquid crystal display described above, the third thinfilm transistor may be a common transistor connecting the gateelectrodes of the plurality of first thin film transistors to the shortring.

[0034] Further, above objects are achieved by an active matrix typeliquid crystal display comprising a switching element formed for each ofa plurality of pixels decided by a plurality of bus lines, and anelectrostatic protection element portion formed between the adjacent buslines, wherein the electrostatic protection element portion comprises afirst thin film transistor having a source or a drain electrodesconnected to one of the adjacent bus lines and the drain or the sourceelectrode connected to the other of the bus lines, a conductive materialconnected to a gate electrode of the first thin film transistor, asecond thin film transistor having a source or a drain electrodeconnected to one of the bus lines, the drain or the source electrodeconnected to the conductive material, and a gate electrode electricallyfloated, and a third thin film transistor having a source or a drainelectrode connected to the other of the bus lines, the drain or thesource electrode connected to the conductive material, and a gateelectrode electrically floated.

[0035] In the liquid crystal display of the present invention above, thegate electrode of the first transistor can be connected to theconductive material via capacitor. Also, a channel length of at leastone of the second and the third thin film transistors can be shorterthan a channel length of the first thin film transistor.

[0036] In the conventional electrostatic protection circuitshort-circuiting the gate electrodes (G) of the second and the thirdTFT's 532 and 534 with the bus line 502 and the short ring 506respectively as shown in FIG. 30, the current does not flow in thesecond and the third TFT's 532 and 534 in reality and the electrostaticprotection circuit is used only for controlling the gate potential ofthe first TFT 530. On the other hand, the first and the second resistorsor the second and the third TFT's of the present invention show atwo-way conductivity between the bus line and the short ring, therebyenabling the current to flow. Thus, the first and the second resistorsor the second and the third TFT's have a function of preliminarilyreleasing the charge due to static electricity before the first TFT forprimarily running the current sufficiently conducts. In other words,since the current preliminarily flows in the second and the third TFT's,the load on the first TFT can be reduced and the redundancy of theelectrostatic protection circuit can be improved.

[0037] Further, the gate electrode of the first TFT of the presentinvention is connected with the bus line and the short ring viacapacitors and the potential of the gate electrode gently varies for atime required to charge and discharge these capacitors. Therefore,according to the structure of the present invention, gentle staticelectricity can sufficiently be dealt with. When the capacitor isinserted between the gate electrode of the first TFT and a commonconductor between the second and the third TFT, a reaction becomesgentle as a whole further and the efficiency as the electrostaticprotection element is improved.

[0038] Furthermore, the structure shown in FIG. 30 has more number ofelements than the structure shown in FIGS. 29a and 29 b and theredundancy is improved. However, for example, if the gate electrode (G)and the drain electrode (D) of the second TFT 532 are short-circuitedand at the same time the gate electrode (G) and the drain electrode (D)of the first TFT 530 are short-circuited, the function as theelectrostatic protection circuit is lost. Similarly, when the gateelectrode (G) and the drain electrode (D) of the third TFT 534 areshort-circuited and at the same time the gate electrode (G) and thedrain electrode (D) of the first TFT 530 are short-circuited, or whenthe gate electrode (G) and the drain electrode (D) of the second TFT 532are short-circuited and at the same time the gate electrode (G) and thedrain electrode (D) of the third TFT 530 are short-circuited, thefunction as the electrostatic protection circuit is also lost. In otherwords, according to the circuit shown in FIG. 30, if the elements in thecircuit are short-circuited at two places as described above, a defectoccurs.

[0039] On the contrary, for example, describing this embodiment withreference to FIG. 3, in the structure according to the presentinvention, if the gate electrode (G) and the source electrode (S) of thesecond TFT 38 are short-circuited and the gate electrode (G) and thedrain electrode (D) of the second TFT 38 are also short-circuited and atthe same time the gate electrode (G) and the drain electrode (D) of thefirst TFT 32 are short-circuited, the function as the electrostaticprotection circuit is lost. Similarly, when the gate electrode (G) andthe source electrode (S) of the third TFT 40 are short-circuited, andthe gate electrode (G) and the drain electrode (D) of the third TFT 40are also short-circuited and at the same time the gate electrode (G) andthe drain electrode (D) of the first TFT 32 are short-circuited, or whenthe gate electrode (G) and the source electrode (S) of the second TFT 38are short-circuited, the gate electrode (G) and the drain electrode (D)of the second TFT 38 are also short-circuited, the gate electrode (G)and the drain electrode (D) of the second TFT 38 are alsoshort-circuited, the gate electrode (G) and the source electrode (S) ofthe third TFT 40 are also short-circuited, and at the same time the gateelectrode (G) and the drain electrode (D) of the third TFT 40 areshort-circuited, the function as the electrostatic protection circuit islost. In other words, according to the specific circuit of the presentinvention shown in FIG. 3, when the elements in the circuitshort-circuit at more than three places, then the function stops for thefirst time as the electrostatic protection circuit. Thus, since the gatein the electrostatic protection circuit according to the presentinvention is in a floating state, the redundancy for a shortage of thestructuring elements is also superior.

[0040] Further, above objects are achieved by an active matrix typeliquid crystal display comprising a switching element formed for each ofa plurality of pixels decided by a plurality of bus lines, a short ringconnected to the plurality of bus lines, and an electrostatic protectionelement portion formed between each of the plurality of bus lines andthe short ring, wherein the electrostatic protection element portioncomprises a plurality of metal layers, an insulating layer formed on theplurality of metal layers, a contact hole formed by opening theinsulating layer on the plurality of metal layers, and a connectinglayer electrically connecting between the metal layers via the contacthole.

[0041] Furthermore, above objects are achieved by an active matrix typeliquid crystal display comprising, a switching element formed for eachof a plurality of pixels decided by a plurality of bus lines, and anelectrostatic protection element portion formed between the adjacent buslines, wherein the electrostatic protection element portion comprises aplurality of metal layers, an insulating layer formed on the pluralityof metal layers, a contact hole formed by opening the insulating layeron the plurality of metal layers, and a connecting layer electricallyconnecting between the metal layers via the contact hole.

[0042] According to the present invention, the contact holes are formedon the protection film on the gate bus line or the data (drain) bus lineand the short ring and each of the bus lines are electrically connectedvia the contact holes. A contact resistance generated between differentmetals (for example, Ti and ITO) in this structure can obtain the ohmiccontact by selecting materials and the resistance value of the resistivecomponent can also be controlled by the number or the size of thecontact holes, or by the subsequent treatment processes for theunderlying metal. The metal contact is certainly not limited to theohmic contact and a resistive device having a non-linear characteristiccan be arranged by the shot-key connection.

[0043] Since the anti-electrostatic element formed according to thepresent invention is easy to control the resistance (current control)and the structure is simple as well, a stable resistive component can beheld. Further, since an arbitrary resistive component can be formed bythe method previously described, the array inspection can be possibleand a sufficient protective function against static electricity can alsobe held by constructing the resistive component.

BRIEF DESCRIPTION OF THE DIAGRAMS

[0044]FIG. 1 is a diagram showing a schematic structure of a liquidcrystal display according to a first embodiment of the presentinvention.

[0045]FIGS. 2a and 2 b are diagrams showing a circuit structure and anoperation of an electrostatic protection element section according tothe first embodiment of the present invention.

[0046]FIG. 3 is a diagram showing a circuit structure of anelectrostatic protection element which is a characteristic component ofa liquid crystal display according to a second embodiment of the presentinvention.

[0047]FIGS. 4a, 4 b and 4 c are diagrams showing a structure of theelectrostatic protection circuit according to the second embodiment ofthe present invention.

[0048]FIG. 5 is a diagram showing an example of a variation of theelectrostatic protection circuit of the liquid crystal display accordingto the second embodiment of the present invention.

[0049]FIG. 6 is a diagram showing a state of an electrostatic protectioncircuit of a liquid crystal display according to a third embodiment ofthe present invention when viewing toward a substrate.

[0050]FIG. 7 is a diagram showing a circuit structure of a electrostaticprotection element section which is the characteristic component of aliquid crystal display according to a fourth embodiment of the presentinvention.

[0051]FIGS. 8a, 8 b and 8 c are diagrams showing a structure of theelectrostatic protection circuit according to the fourth embodiment ofthe present invention.

[0052]FIG. 9 is a diagram showing an example of a variation of thestructure of the electrostatic protection circuit according to thefourth embodiment of the present invention.

[0053]FIG. 10 is a diagram showing an example of a variation of theelectrostatic protection circuit according to the fourth embodiment ofthe present invention.

[0054]FIG. 11 is a diagram showing an other example of the variation ofthe electrostatic protection circuit according to the fourth embodimentof the present invention.

[0055]FIG. 12 is a diagram showing a circuit of an electrostaticprotection element section of a liquid crystal display according to afifth embodiment of the present invention.

[0056]FIG. 13 is a diagram showing an example of a variation of theelectrostatic protection circuit of the liquid crystal display accordingto the fifth embodiment of the present invention.

[0057]FIG. 14 is a diagram showing a circuit of an electrostaticprotection element section of a liquid crystal display according to asixth embodiment of the present invention.

[0058]FIG. 15 is a diagram showing a structure of the electrostaticprotection circuit of the liquid crystal display according to the sixthembodiment of the present invention.

[0059]FIG. 16 is a diagram showing an example of a variation of theelectrostatic protection circuit of the liquid crystal display accordingto the sixth embodiment of the present invention.

[0060]FIG. 17 is a diagram showing a structure of an example of avariation of the electrostatic protection circuit of the liquid crystaldisplay according to the sixth embodiment of the present invention.

[0061]FIG. 18 is a diagram showing a circuit of an electrostaticprotection element section of a liquid crystal display according to aseventh embodiment of the present invention.

[0062]FIG. 19 is a diagram showing a structure of the electrostaticprotection circuit of the liquid crystal display according to theseventh embodiment of the present invention.

[0063]FIG. 20 is a diagram showing an example of a variation of theelectrostatic protection circuit of the liquid crystal display accordingto the seventh embodiment of the present invention.

[0064]FIG. 21 is a diagram showing a structure of an example of avariation of the electrostatic protection circuit of the liquid crystaldisplay according to the seventh embodiment of the present invention.

[0065]FIG. 22 is a diagram showing a structure of an example of avariation of the electrostatic protection circuit of the liquid crystaldisplay according to the first through the seventh embodiments of thepresent invention.

[0066]FIGS. 23a and 23 b are diagrams showing a structure of anelectrostatic protection circuit of a liquid crystal display accordingto an eighth embodiment of the present invention.

[0067]FIGS. 24a and 24 b are diagrams showing a structure of an exampleof a variation of the electrostatic protection circuit of the liquidcrystal display according to the eighth embodiment of the presentinvention.

[0068]FIG. 25 is a diagram showing a fabrication process of theelectrostatic protection circuit of the liquid crystal display accordingto the eighth embodiment of the present invention.

[0069]FIG. 26 is a diagram showing a structure of other example of thevariation of the electrostatic protection circuit of the liquid crystaldisplay according to the eighth embodiment of the present invention.

[0070]FIG. 27 is a diagram showing a structure of an example of anapplication of the electrostatic protection circuit of the liquidcrystal display according to the eighth embodiment of the presentinvention.

[0071]FIG. 28 is a diagram showing a structure of the electrostaticprotection circuit of a conventional liquid crystal display.

[0072]FIGS. 29a and 29 b are diagrams showing a structure of theelectrostatic protection circuit of the conventional liquid crystaldisplay.

[0073]FIG. 30 is a diagram showing a structure of the electrostaticprotection circuit of the conventional liquid crystal display.

[0074]FIG. 31 is a diagram showing a structure of the electrostaticprotection circuit of the conventional liquid crystal display.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0075] A liquid crystal display according to a first embodiment of thepresent invention is described with reference to FIG. 1, FIG. 2a andFIG. 2b. First, a schematic structure of the liquid crystal displayaccording to this embodiment is described with reference to FIG. 1. FIG.1 shows a part of a substrate 1 on an array side of this liquid crystaldisplay viewing toward a substrate surface. It will be noted that insideof a pixel area shows an equivalent circuit for driving liquid crystal.On the substrate 1 on the array side, a plurality of gate bus lines 2extending in the horizontal direction in the diagram are formed inparallel in the vertical direction. Furthermore, although omitted in thediagram, an insulation film is formed on the plurality of gate bus lines2, and a plurality of data bus lines 4 are formed on the insulation filmin substantially orthogonal to the gate bus lines 2. Each area decidedby the gate bus lines 2 and the data bus lines 4 which crossorthogonally to each other in a matrix shape becomes a pixel area, and aTFT 6 and a display electrode 8 are formed in each pixel area. A gateelectrode of the TFT 6 is connected to a predetermined gate bus line 2,a drain electrode is connected to a predetermined data bus line 4, and asource electrode is connected to the display electrode 8 in the pixelarea. A dotted line 14 in the diagram shows an end portion of anopposing substrate. On the opposing substrate side, common electrode 12is formed. Liquid crystal 10 is sealed between the substrate 1 on thearray side and the opposing substrate.

[0076] The TFT 6 in which the gate electrode is connected to the gatebus line 2 is set to “On” state by a scanning signal outputted to thepredetermined gate bus line 2, and the voltage based on a gradationsignal outputted to the data bus line 4 is applied to a pixel electrode8. On the other hand, a predetermined voltage is also applied to thecommon electrode 12 on the opposing substrate side and the liquidcrystal between the pixel electrode 8 and the common electrode 12 isdriven by the voltage applied to the pixel electrode 8 and the commonelectrode 12.

[0077] An external output electrode 16 is formed at the end portion ofeach gate bus line 2 and an external output electrode 18 is also formedat the end portion of each data bus line 4. A short ring 20 which is acomponent of an electrostatic protection circuit is formed at theexternal surrounding of the external output electrodes 16 and 18. Theshort ring 20 has a common wiring 22 on the gate bus line side and acommon wiring 24 on the data bus line side. An electrostatic protectionelement section 28 which is a component of the electrostatic protectioncircuit is formed between the common wiring 22 on the gate bus line sideand the external output electrode 16 on each of the gate bus line 2. Onthe other hand, an electrostatic protection element section 30 which isa component of the electrostatic protection circuit is formed betweenthe common wiring 24 on the data bus line side and the external outputelectrode 18 on each data bus line 4.

[0078] Next, a circuit structure and operation of the electrostaticprotection element sections 28 and 30 according to this embodiment isdescribed with reference to FIG. 2a. It will be noted that since thestructure and operation of the electrostatic protection element section28 and the electrostatic protection element section 30 are the same,hereinafter, the electrostatic protection element section 28 isdescribed as an example. The electrostatic protection element section 28has a TFT 32, a first resistor 34 and a second resistor 36. A sourceelectrode (S) of the TFT 32 which is an electrostatic protection elementis connected to the external output electrode 16 on the gate bus line 2.On the other hand, a drain electrode (D) is connected to the commonwiring 22. A gate electrode (G) of the TFT 32 is connected to theexternal output electrode 16 by the first resistor 34 and at the sametime, the gate electrode (G) of the TFT 32 is connected to the commonwiring 22 by the second resistor 36. When a positive high voltagegenerates to the bus line with respect to the common wiring 22 due tostatic electricity, the voltage with the value which divides the highvoltage generated due to the static electricity with the first resistor34 and the second resistor 36 is applied to the gate electrode (G) ofthe TFT 32. As a result, since the conductivity of the TFT 32 rapidlyincreases, electric charges due to static electricity are released viathe TFT 32. At this time, the electric charges are released not only viathe TFT 32 but also via the first and the second resistors 34 and 36.The current flowing in the TFT 32 is relieved in comparison with thecase where the TFT is a single unit as shown in FIGS. 29a and 29 b andis further superior in redundancy as the electrostatic protectionelement to a protection circuit shown in FIG. 30. Therefore, the liquidcrystal display having the electrostatic protection circuit which is noteasily destroyed by static electricity and in which TFT tests can alsobe sufficiently performed can be fabricated.

[0079] Next, a circuit structure of the electrostatic protection elementsections 28(=30) according to another example is described withreference to FIG. 2b. The electrostatic protection element section 28has the TFT 32, the first resistor 34, the second resistor 36, aconductor 42, and a capacitor 100.

[0080] The gate electrode (G) of the TFT 32 is connected to theconductor 42 which is electrically insulated from either the externaloutput electrode 16 of the bus line 2 or the common wiring 22. The firstresistor 34 is connected between the external output electrode 16 andthe conductor 42. The second resistor 36 is connected between the commonwiring 22 and the conductor 42.

[0081] The capacitor 100 is formed between the conductor 42 and the gateelectrode (G) of the TFT 32. When static electricity is generated, theoperation of the TFT 32 becomes gentle due to the capacitor 100.Further, since the capacitor 100 is added, the redundancy againstdefects due to shortage is also improved.

[0082] Next, a liquid crystal display according to a second embodimentof the present invention is described with reference to FIG. 3 throughFIG. 5. Since a schematic structure of this liquid crystal display issimilar to FIG. 1 used in the first embodiment, description is omitted,and a circuit structure of the electrostatic protection element sections28 and 30 which are characteristic components is described withreference to FIG. 3. The electrostatic protection element section 28 hasthe first through the third TFT's 32, 38 and 40, and a conductor 42. Thesource electrode (S) of the first TFT 32 which is the electrostaticprotection element is connected to the external output electrode 16 ofthe bus line 2, and the drain electrode (D) on the other side isconnected to the common wiring 22. The gate electrode (G) of the firstTFT 32 is connected to the conductor 42 which is electrically insulatedfrom either the external output electrode 16 of the bus line 2 or thecommon wiring 22. On the other hand, the source electrode (S) of thesecond TFT 38 is connected to the external output electrode 16 and thedrain electrode (D) on the other side is connected to the conductor 42.Further, the drain electrode (D) of the third TFT 40 is connected to theconductor 42 and the source electrode (S) on the other side is connectedto the common wiring 22. Furthermore, the gate electrode (G) of thesecond and the third TFT's 38 and 40 are not connected to any patternsand are isolated. When a positive high voltage is generated to the busline with respect to the common wiring 22 by static electricity, a highvoltage internally divided by each parasitic capacitor (C2 _(gs), C2_(gd), C3 _(gs), C3 _(gd)) is applied to the gate electrodes (G) of thesecond and the third TFT's 38 and 40 and a channel is formed in thesecond and third TFT's 38 and 40. As a result, the current flows throughthe second and the third TFT's 38 and 40, and the potential of theconductor 42 also increases. Hence, a channel is formed in the first TFT32 and the conductivity increases, thereby releasing the electriccharges due to static electricity. According to this embodiment, sincethe current preliminarily flows to the second and the third TFT's 38 and40 in this manner, a load on the first TFT 32 is reduced and theredundancy of the electrostatic protection circuit can be improved.Further, the gate electrode (G) of the first TFT 32 is connected to theexternal output electrodes 16 and 18 via the capacitors and to thecommon wirings 22 and 24 of the short ring 20, and the potential of thegate electrode (G) gently varies for only the time required to chargeand discharge these capacitors. Therefore, according to the structure inthis embodiment, gentle static electricity can be sufficiently dealtwith.

[0083] Since the electric charges are released through a plurality ofpaths in this manner, in comparison with the case in the past wherethere is a single TFT, the load to the first TFT is relieved. Further,since the redundancy as the electrostatic protection element increases,the liquid crystal display having the electrostatic protection circuitwhich is not easily destroyed by static electricity and in which TFTtests can also be performed sufficiently can be fabricated.

[0084] Next, a structure of the electrostatic protection circuitaccording to this embodiment is described with reference to FIGS. 4a, 4b and 4 c. FIG. 4a shows a single electrostatic protection circuit onthe substrate 1 on the array side viewing toward the substrate surface.FIG. 4b shows a cross section cut at a line A-A′ in FIG. 4a. FIG. 4cshows a cross section cut at a line B-B′ in FIG. 4a.

[0085] In FIG. 4a, the electrostatic protection element section 28 (or30, hereinafter, description omitted) is formed between the commonwiring 22 (or 24, hereinafter, description omitted) extending verticallyin the left side of the diagram and the external output electrode 16 (or18, hereinafter, description omitted). As shown in FIGS. 4b and 4 c,when the gate bus line 2 and the gate electrode of the TFT 6 (refer toFIG. 1) in the pixel area are formed on a glass substrate 50, the gateelectrodes (G) of the first through the third TFT's 32, 38 and 40 arealso simultaneously formed. The gate electrodes (G) of the second andthe third TFT's 38 and 40 are formed electrically floated from otherwiring structures. A gate insulation film 52 is formed on the gateelectrodes (G) and the glass substrate 50. An operating semiconductorlayer 44 made of a-Si is patterned individually on the gate insulationfilm 52 formed on each gate electrode (G) of the first through the thirdTFT's 32, 38 and 40. The data (drain) bus line 4 and a source/drainelectrode patterned when simultaneously forming the external outputelectrode 16 are formed on both sides sandwiching each operatingsemiconductor layer 44. End portions of each source/drain electrode lieover each operating semiconductor layer 44. When viewing toward thesubstrate surface, an area, where the end portion of each source/drainelectrode and the lower layer gate electrode (G) overlap, is formed.Further, the short ring 22 is also simultaneously formed when the databus line 4 is formed. A passivation film 54 is formed on a whole surfaceof the element formation area.

[0086] A contact hole 56 is formed by removing the passivation film 54on substantially the center of the source/drain electrode between thesecond and the third TFT's 38 and 40. Similarly, a contact hole 58 isformed by removing the gate insulation film 52 and the passivation film54 on an end portion of the gate electrode of the first TFT 32. Aportion substantially the center of the source/drain electrode betweenthe second and the third TFT's 38 and 40 and the gate electrode of thefirst TFT 32 are connected by an ITO layer 43 constructing a part of theconductor via the two contact holes 56 and 58. In this example, an ITOlayer 42 which is a component of the conductor 42 is simultaneouslyformed when patterning the ITO as a transparent electrode for forming adisplay electrode in each pixel area.

[0087] In the structure shown in FIGS. 4a, 4 b and 4 c, both of theexternal output electrodes 16 and 18 and the common wirings 22 and 24 ofthe short ring 20 are formed simultaneously with the formation of thedata bus line 4 and by the same formation material as the data bus line4. However, this is not essential. For example, as shown in FIG. 5, theexternal output electrodes 16 and 18 and the short rings 22 and 24 mayalso be formed simultaneously with the formation of the gate bus line 2and by the same metal layer as the gate bus line 2. FIG. 5 shows a statein which an electrostatic protection circuit on the substrate 1 on thearray side is viewed toward the substrate surface. As shown in FIG. 5, asource electrode 70 of the first TFT 32 to be connected with theexternal output electrodes 16 and 18 is connected at an ITO layer 72which is a layer when forming the display electrode, via a contact hole74 formed on an end portion of the source electrode 70 and a contacthole 76 formed on the external output electrodes 16 and 18. Similarly, asource electrode 60 of the second TFT 38 to be connected with theexternal output electrodes 16 and 18 is connected by an ITO layer 62which is a layer when forming the display electrode, via a contact hole64 formed on an end portion of the source electrode 60 and a contacthole 66 formed on the external output electrodes 16 and 18. Further, inthe same manner, a drain electrode 80 of the first TFT 32 to beconnected with the common wirings 22 and 24 of the short ring 20 and asource electrode 90 of the third TFT 40 are respectively connected byITO layers 82 and 92 which are layers when forming the displayelectrode, via contact holes 84 and 94 formed on end portions of thedrain electrode 80 and the source electrode 90 and contact holes 86 and96 formed on the common wirings 22 and 24 respectively.

[0088] Next, a liquid crystal display according to a third embodiment ofthe present invention is described with reference to FIG. 6. FIG. 6shows a state of the electrostatic protection circuit on the substrate 1on the array side when viewing toward the substrate surface. The liquidcrystal display according to this embodiment also has distinctivecharacteristics in the electrostatic protection circuit and since othercomponents are the same as the components described in the firstembodiment with reference to FIG. 1, descriptions for the othercomponents are omitted. Further, in the electrostatic protection elementsection, components having the similar function and operation to thefirst and the second embodiments are also referred by the same codes anddescriptions are omitted. The electrostatic protection circuit accordingto this embodiment has a distinctive characteristic in forming theelectrostatic protection element sections 28 and 30 described in thesecond embodiment with reference to FIGS. 4a, 4 b and 4 c between theadjacent bus lines, thereby not forming the short ring 20. In otherwords, the source electrode of the first TFT 32 is connected to one ofthe two adjacent bus lines 2 (or 4, hereinafter, description omitted),and the drain electrode is connected to the other of the two adjacentbus lines 2. Further, the source electrode of the second TFT 38 isconnected to one of the two adjacent bus lines 2 and the sourceelectrode of the third TFT 40 is connected to the other of the twoadjacent bus lines 2. Except for the differences in the structure above,the similar effects to the second embodiment can be obtained by theelectrostatic protection circuit according to this embodiment.

[0089] Next, a liquid crystal display according to a fourth embodimentof the present invention is described with reference to FIG. 7 throughFIG. 11. Since the schematic structure of this liquid crystal display issimilar to FIG. 1 used in the first embodiment, description is omitted,and the circuit structure of the electrostatic protection elementportions 28 and 30 which are characteristic components is described withreference to FIG. 7. However, components exhibiting the similarfunctions and operations to the structures shown in FIGS. 3, 4a, 4 b and4 c are referred by the same codes and descriptions are omitted.

[0090] The electrostatic protection element portion 28 according to thisembodiment, as is the case in the second embodiment, has the firstthrough the third TFT's 32, 38 and 40 and the conductor 42. Thedifference from the second embodiment is to have a capacitor 100. Thecapacitor 100 is formed between the conductor 42 and the gate electrode(G) of the first TFT 32. When static electricity is generated, theoperation of the first TFT 32 becomes gentle due to the capacitor 100 incomparison with the second and the third TFT's 38 and 40. Therefore, inthe case of static electricity generating sharp pulse-like variations involtage, the current first flows to the second and the third TFT's 38and 40, thereby protecting the first TFT 32. Further, in the case ofstatic electricity generating a gentle increase in voltage, followingthe second and the third TFT's 38 and 40, the first TFT 32 operates andcontributes for releasing the electric charges. According to thisembodiment, since the current preliminarily flows to the second and thethird TFT's 38 and 40 in this manner, the load on the first TFT 32 isreduced and the redundancy of the electrostatic protection circuit canbe improved. Furthermore, since the gate electrode (G) of the first TFT32 is connected with the external output electrodes 16 and 18 and thecommon wirings 22 and 24 of the short ring 20 via the capacitor, thepotential of the gate electrode (G) varies gently for a time required tocharge and discharge these capacitors. Therefore, according to thestructure in this embodiment, gentle static electricity can besufficiently dealt with. Also, according to this embodiment, since thecapacitor 100 is inserted between the gate electrode (G) of the firstTFT 32 and the common conductor 42 between the second and the thirdTFT's 38 and 40, even if the difference in potential between theexternal output electrodes 16 and 18 and the common wirings 22 and 24 ofthe short ring 20 is reduced, a state of continuity can be kept stilllonger for a time required to charge and discharge the capacitor 100,and the efficiency in charge release can be further improved. Further,since the capacitor 100 is added, the redundancy against defects due toshortage is also improved. In this embodiment, since the electriccharges are also released through a plurality of paths, the redundancyas the electrostatic protection element increases in comparison with thecase in the past where there is a single TFT, therefore the protectioncircuit which is not easily destroyed by static electricity can beformed.

[0091] Next, a structure of the electrostatic protection circuitaccording to this embodiment is described with reference to FIGS. 8a, 8b and 8 c. FIG. 8a shows a state of a single electrostatic protectioncircuit on the substrate 1 on the array side when viewing toward thesubstrate. FIG. 8b shows a cross section cut at a line A-A′ in FIG. 8a.FIG. 8c shows a cross section cut at a line B-B′ in FIG. 8a.

[0092] In FIG. 8a, the electrostatic protection element portion 28 isformed between the common wiring 22 extending vertically in the leftside of the diagram and the external output electrode 16. As shown inFIGS. 8b and 8 c, when the gate bus line 2 and the gate electrode of theTFT 6 (refer to FIG. 1) in the pixel area are formed, the gateelectrodes (G) of the first through the third TFT's 32, 38 and 40 arealso simultaneously formed on the glass substrate 50. The gateelectrodes (G) of the second and the third TFT's 38 and 40 are formedelectrically floated from other wiring structures. The gate insulationfilm 52 is formed on the gate electrodes (G) and the glass substrate 50.The operating semiconductor layer 44 made of a-Si is patternedindividually on the gate insulation film 52 formed on each gateelectrode (G) of the first through the third TFT's. The source/drainelectrode is simultaneously patterned when the data (drain) bus line 4and external output electrode 16 are formed on both sides sandwichingeach of the operating semiconductor layer 44. The end portions of eachsource/drain electrode are formed lying over each operatingsemiconductor layer 44. Further, the short ring 22 is alsosimultaneously formed when the data bus line 4 is formed. Thepassivation film 54 is formed on the whole surface of the elementformation area.

[0093] The source/drain electrode between the second and the third TFT's38 and 40 functions as the conductor 42 and also forms the capacitor 100between the source/drain electrode and the gate electrode (G) of thefirst TFT 32 extending to the lower part of the conductor 42.

[0094] In the structure shown in FIGS. 8a, 8 b and 8 c, the externaloutput electrodes 16 and 18 and the short rings 22 and 24 are formedsimultaneously with the formation of the data bus line 4 and by the sameformation material as the data bus line 4. However, this is notessential. For example, as shown in FIG. 9, the external outputelectrodes 16 and 18 and the short rings 22 and 24 may also be formedsimultaneously by the same metal layer as the gate bus line 2 when thegate bus line 2 is formed. The structure shown in FIG. 9 can be obtainedby changing the connections of the wirings in the same manner asdescribed with reference to FIG. 5.

[0095] Next, an example of a variation of the electrostatic protectioncircuit according to this embodiment is described with reference to FIG.10 and FIG. 11. In the first and the second embodiments and thisembodiment, the short ring 20 and the electrostatic protection elementsections 28 and 30 are arranged outside the external output electrodes16 and 18 on the substrate on the array side. Therefore, the short ring20 and the electrostatic protection element sections 28 and 30 can beremoved by a beveling process after panel scribing. On the other hand,if the short ring 20 is arranged inside the external output electrodes16 and 18, the glass substrate can be efficiently utilized without wasteby reducing an area for scribing on the glass substrate. In this case,the short ring 20 and the electrostatic protection element sections 28and 30 remain in the liquid crystal panel even after panel scribing andeach of the bus lines 2 and 4 is short-circuited via the electrostaticprotection circuit. However, the resistance is so large that aninterference between each bus line can be ignored and the quality of aproduct is not at all affected. A position to form the short ring 20 canbe considered in the same manner as in all embodiments to be describedhereinafter.

[0096]FIG. 10 shows an example of the electrostatic protection circuitstructure forming the common wiring 24 of the short ring 20 inside theexternal output electrode 18 of the data bus line 4. The electrostaticprotection element section 30 is formed between the common wiring 24extending vertically in the diagram and the pixel area (opposite side ofthe external output electrode 18 with respect to the common wiring 24)which is not identified in the diagram. The gate electrodes (G) of thefirst through the third TFT's 32, 38 and 40 are simultaneously formed onthe glass substrate 50 when the gate bus line 2 and the gate electrodeof the TFT 6 (refer to FIG. 1) in the pixel area are formed. The gateelectrodes (G) of the second and the third TFT's 38 and 40 are formedelectrically floated from the other wiring structures. Further, thecommon wiring 24 is also formed simultaneously when the gate bus line 2is formed. The drain electrode (D) of the first TFT 32 and the drainelectrode (D) of the third TFT 40 are connected to the common wiring 24via a contact hole portion 77.

[0097] The source/drain electrode between the second and the third TFT's38 and 40 functions as the conductor 42 and also forms the capacitor 100between the source/drain electrode and the gate electrode (G) of thefirst TFT 32 extending to the lower part of the conductor 42.

[0098] Further, in this example, the channel lengths of the second andthe third TFT's 38 and 40 are formed shorter than the channel length ofthe first TFT 32. Thus, when static electricity producing extremelysharp pulse-like voltage is generated in the data line 4, the second orthe third TFT's 38 or 40 are first destroyed before the first TFT 32 isdestroyed, thereby protecting the first TFT 32. Therefore, even if anyone of the second and the third TFT's 38 and 40 is destroyed, the databus line 4 and the common wiring 24 do not directly short-circuit and donot provide an obstacle in sequential processes including TFT tests.Furthermore, in this example, the channel lengths of the second andthird TFT's 38 and 40 are the same and are at the same time equal toapproximately half the channel length of the first TFT 32. Also, thechannel widths of the second and the third TFT 38 and 40 are the sameand are at the same time approximately the same width as the channelwidth of the first TFT 32. Therefore, the conductivity of the first TFT32 and the conductivity of the second and the third TFT's 38 and 40 whenobserved serially are approximately the same, and the current can bedivided into approximately halves by the first TFT 32 and the second andthe third TFT's 38 and 40.

[0099]FIG. 11 shows an example of the electrostatic protection circuitstructure forming the common wiring 22 of the short ring 20 inside theexternal output electrode 16 of the gate bus line 2. The electrostaticprotection element section 28 is formed between the common wiring 22extending vertically in the diagram and the pixel area (opposite side ofthe external output electrode 16 with respect to the common wiring 22)which is not identified in the diagram. The gate electrodes (G) of thefirst through the third TFT's 32, 38 and 40 are simultaneously formed onthe glass substrate 50 when the gate bus line 2 and the gate electrodeof the TFT 6 (refer to FIG. 1) in the pixel area are formed. The gateelectrodes (G) of the second and the third TFT's 30 and 40 are formedelectrically floated from the other wiring structures.

[0100] The source/drain electrodes of the first through the third TFT's32, 38 and 40 and the common wiring 22 are formed simultaneously withthe formation of the data bus line and by the same formation material asthe data bus line. The source electrode (S) of the first TFT and thesource electrode (S) of the second TFT 38 are connected to the gate busline 2 via contact hole portions 78 and 79 respectively.

[0101] The source/drain electrode between the second and the third TFT's38 and 40 functions as the conductor 42 and also forms the capacitor 100between the source/drain electrode and the gate electrode (G) of thefirst TFT extending to the lower part of the conductor 42.

[0102] Further, in this example, as is the case shown in FIG. 10, thechannel lengths of the second and third TFT's 38 and 40 are the same andare at the same time equal to approximately half the channel length ofthe first TFT 32. Also, the channel widths of the second and the thirdTFT 38 and 40 are the same and are at the same time approximately thesame width as the channel width of the first TFT 32. Therefore, theconductivity of the first TFT 32 and the conductivity of the second andthe third TFT's 38 and 40 when observed serially are approximately thesame, and the current can be divided into approximately halves by thefirst TFT 32 and the second and the third TFT's 38 and 40.

[0103] Next, a liquid crystal display according to a fifth embodiment ofthe present invention is described with reference to FIG. 12 and FIG.13. While in the first through the fourth embodiments described above, aset of electrostatic protection element sections are respectively formedin each bus line, the liquid crystal display holding the elements formedin the electrostatic protection element section in common as much aspossible and reducing the number of whole elements is shown in thisembodiment. When a generation ratio of component defects, an areaoccupied by the elements and the like are considered, reducing thenumber of structuring elements as much as possible is more desirable.

[0104] A circuit of the electrostatic protection element sectionaccording to this embodiment is shown in FIG. 12. As shown in FIG. 12,in electrostatic protection element sections 28-1 and 28-2 (or 30-1 and30-2), TFT's 32-1 and 32-2 and the first resistors 34-1 and 34-2 areformed at each of the external output electrodes 16-1 and 16-2 (or 18-1and 18-2). The second resistor 36 is not formed in each of the elementsections 28-1 and 28-2. Instead, the conductor 42, to which theelectrodes (G) of the first TFT's 32-1 and 32-2 are connected, and thecommon wirings 22 and 24 are connected at a single common resistor 37 asthe second resistor. By providing the common resistor 37, the number ofelements structuring the electrostatic protection element sections canbe reduced to {fraction (3/4)} in comparison with the first through thefourth embodiments.

[0105] For example, if a positive high voltage is generated in the busline of the external output electrode 16 against the common wiring 22due to static electricity, the voltage value obtained by dividing thehigh voltage generated due to static electricity by the first resistor34-1 and the common resistor 37 is applied to the gate electrodes (G) ofTFT's 32-1 and 32-2. As a result, since the conductivity of TFT's 32-1and 32-2 rapidly increase, the electric charges due to staticelectricity is released via TFT's 32-1 and 32-2. At this time, since theelectric charges are released not only via TFT's 32-1 and 32-2 but alsovia the first resistors 34-1 and 34-2 and the common resister 37 and thecurrent flowing through the TFT 32-1 is relieved, the redundancy as theelectrostatic protection element increases, thereby realizing theelectrostatic protection circuit which is not easily destroyed by staticelectricity.

[0106] Next, an example of a variation of this embodiment is describedwith reference to FIG. 13. In order to reduce the number of elementsstructuring the electrostatic protection circuits as much as possible,the structure shown in FIG. 12 is further proceeded. The structure shownin FIG. 13 has a distinctive characteristic in using a single commonresistor 37 in common among the electrostatic protection elementsections 28-1 through 28-n (or 30-1 through 30-n) of more than n (n isan integer of more than 3) bus lines.

[0107] In the electrostatic protection element sections 28-1 through28-n provided at each of the external output electrodes 16-1 through16-n, TFT's 32-1 through 32-n and the first resistor 34-1 through 34-nare respectively formed. The second resistor 36 is not formed in each ofthe element sections 21-1 through 28-n. Instead, the conductor 42 towhich the gate electrodes (G) of the first TFT's 32-1 through 32-n areconnected and the common wirings 22 and 24 are connected by the commonresistor 37 as the single second resistor in place of individual secondresistors.

[0108] If the common resistor 37 is used in place of individual secondresistors in the electrostatic protection element sections 28 and 30 ofall the bus lines, the number of structuring elements per a bus line canbe approximately 2 and the number of elements used in the electrostaticprotection circuits according to the first embodiment can be reduced toapproximately half.

[0109] Next, a liquid crystal according to a sixth embodiment of thepresent invention is described with reference to FIG. 14 through FIG.17. While in the liquid crystal display according to the secondembodiment above, a set of electrostatic protection element sections arerespectively formed in each bus line, in this embodiment as is the casein the fifth embodiment, the liquid crystal display holding the elementsformed in the electrostatic protection element section in common as muchas possible and reducing the number of whole elements is shown.

[0110] A circuit of the electrostatic protection element sectionaccording to this embodiment is shown in FIG. 14. As shown in FIG. 14,in electrostatic protection element sections 28-1 and 28-2 (or 30-1 and30-2), the first TFT's 32-1 and 32-2 and the second TFT's 38-1 and 38-2are formed at each of the external output electrodes 16-2 and 16-2 (or18-1 and 18-2). The third TFT 40 is not formed in each of the elementsections 28-1 and 28-2. Instead, the conductor 42 to which theelectrodes (G) of the first TFT's 32-1 and 32-2 are connected and thecommon wirings 22 and 24 are connected at a common TFT 41 as the singlethird TFT in place of the third individual TFT. By providing the commonTFT 41, the number of elements structuring the electrostatic protectionelement sections can be reduced to {fraction (3/4)} in comparison withthe first through the fourth embodiments.

[0111] For example, if a positive high voltage is generated in the busline of the external output electrode 16-1 against the common wiring 22due to static electricity, the high voltage interior-divided by eachparasitic capacitor (C2 _(gs), C2 _(gd), Cc_(gs), Cc_(gd)) is applied tothe second TFT 38-1 and the gate electrode (G) of the common TFT 41 andchannels are formed in the second TFT 38-1 and the common TFT 41. As aresult, the current flows through the second TFT 38-1 and the common TFT41, and the potential of the conductor 42 also increases. Hence, achannel is formed in the first TFT 32-1 and the conductivity increases,thereby releasing the electric charges due to static electricity. Sincethe electric charges are also released through a plurality of paths inthis case, the amount of the electric charges flowing in the first TFT32 is relieved in comparison with the case in the past having a singleTFT. Therefore, the redundancy as the electrostatic protection elementincreases and the protection circuit which can not be easily destroyedby static electricity can be formed.

[0112] Next, the structure of the electrostatic protection circuitaccording to this embodiment is described with reference to FIG. 15.FIG. 15 shows a state of a single electrostatic protection circuit onthe substrate 1 on the array side when viewing toward the substratesurface. In FIG. 15, the electrostatic protection element sections 28-1and 28-2 are formed between the common wiring 22 extending vertically onthe left side of the diagram and the external output electrodes 16-1 and16-2.

[0113] In this example, the conductor 42 extends vertically in thediagram and is connected to the first TFT 32-1 of the electrostaticprotection element section 28-1 side by the ITO layer 43 via contactholes 56-1 and 58-1. Further, the conductor 42 is connected to the firstTFT 32-2 of the electrostatic protection element section 28-2 side bythe ITO layer 43 via contact holes 56-2 and 58-2.

[0114] The operating semiconductor layer 44 made of a-Si is patterned onthe gate insulation film on the gate electrode (G) of the common TFT 41.The drain electrode (D) of the common TFT 41 pulled out fromsubstantially the center portion of the conductor 42 is connected atboth sides sandwiching the operating semiconductor layer 44. The sourceelectrode of the common TFT 41 is connected to the common wirings 22 and24. End portions of the source/drain electrode of the common TFT 41 lieover the operating semiconductor layer 44 and areas where end portionsof each source/drain electrode and the under-layer gate electrodes (G)overlap are formed. The conductor 42, the external output electrodes16-1 and 16-2 and the common wirings 22 and 24 are simultaneously formedwhen the data bus line 4 is formed.

[0115] Next, an example of a variation of this embodiment is describedwith reference to FIG. 16. In order to reduce the number of elementsstructuring the electrostatic protection circuits as many as possible,the structure shown in FIG. 15 is further proceeded. The structure shownin FIG. 16 has a distinctive characteristic in using a single common TFT41 among the electrostatic protection element sections 28-1 through 28-n(or 30-1 through 30-n) of more than n (n is an integer of more than 3)bus lines.

[0116] In the electrostatic protection element sections 28-1 through28-n provided at each of the external output electrodes 16-1 through16-n, the first TFT's 32-1 through 32-n and the second TFT's 38-1through 38-n are respectively formed. The third TFT 40 is not formed ineach of the element sections 28-1 through 28-n. Instead, the conductor42 to which the gate electrodes (G) of the first TFT's 32-1 through 32-nare connected and the common wirings 22 and 24 are connected at thecommon TFT 41 as the single third TFT in place of individual third TFT.

[0117] If the common TFT 41 is used in place of the third TFT 40 in theelectrostatic protection element sections 28 and 30 of all the buslines, the number of structuring elements per a bus line can beapproximately 2 and the number of elements used in the electrostaticprotection circuits according to the second embodiment can be reduced toapproximately half.

[0118] Next, the structure of the electrostatic protection circuitaccording to this embodiment is described with reference to FIG. 17.FIG. 17 shows a state of a single electrostatic protection circuit onthe substrate 1 on the array side when viewing toward the substratesurface. In FIG. 17, the electrostatic protection element sections 28-1and 28-n are formed between the common wiring 22 extending vertically inthe left side on the diagram and the external output electrodes 16-1 and16-n.

[0119] In this example, the conductor 42 extends vertically in thediagram and is connected to the gate electrodes of a plurality of thefirst TFT's 32-1 through 32-n. Further, the second TFT's 38-1 through38-n are connected to the conductor 42 by the ITO layer 43 via contactholes. Since the structure of the common TFT 41 is the same as thestructure described with reference to FIG. 15, description is omitted.The drain electrode of the common TFT 41 is connected to the conductor42 by the ITO layer 43 via contact holes and the source electrode isconnected to the common wirings 22 and 24.

[0120] Next, a liquid crystal display according to a seventh embodimentof the present invention is described with reference to FIG. 18 throughFIG. 21. While a set of electrostatic protection element sections arerespectively formed in each bus line in the liquid crystal displayaccording to the third embodiment above, in this embodiment as is thecase in the fifth and sixth embodiments, the liquid crystal displayholding the elements formed in the electrostatic protection elementsection in common as much as possible and reducing the number of wholeelements is shown.

[0121] The circuit of the electrostatic protection element sectionaccording to this embodiment is shown in FIG. 18. As shown in FIG. 18,capacitors 100-1 and 100-2 are formed in each of the electrostaticprotection element sections 28-1 and 28-2. The third TFT 40 is notformed in each of the element sections 28-1 and 28-2. Instead, theconductor 42 to which the electrodes (G) of the first TFT's 32-1 and32-2 are connected and the common wirings 22 and 24 are connected at acommon TFT 41 as the single third TFT in place of the third individualTFT. By providing the common TFT 41, the number of elements structuringthe electrostatic protection element sections can be reduced to{fraction (3/4)} in comparison with the first through the fourthembodiments.

[0122] According to this embodiment, by having the capacitor 100,operations of the first TFT's 32-1 and 32-2 when static electricity isgenerated also become gentle in comparison with operations of the secondTFT's 38-1 and 38-2 and the common TFT 41. Therefore, in the case ofstatic electricity generating sharp pulse-like variations in voltage,the current first flows to the second TFT's 38-1 and 38-2 and the commonTFT 41, thereby protecting the first TFT's 32-1 and 32-2. Further, inthe case of static electricity gently increasing in voltage, the firstTFT's 32-1 and 32-2 operate following the second TFT's 38-1 and 38-2 andthe common TFT 41 and contribute to the release of the electric charge.According to this embodiment, since the current preliminarily flows tothe second TFT's 38-1 and 38-2 and the common TFT 41, the load on thefirst TFT's 32-1 and 32-2 is reduced, thereby increasing the redundancyof the electrostatic protection circuit. Further, the gate electrodes ofthe first TFT's 32-1 and 32-2 are respectively connected with theexternal output electrodes 16-1, 18-1, 16-2 and 18-2 and the commonwirings 22 and 24 of the short ring 20 via the capacitors, and thepotential of the gate electrode (G) gently varies for a time required tocharge and discharge these capacitors. Therefore, according to thestructure of this embodiment, even gentle static electricity can besufficiently dealt with. Furthermore, in this embodiment, since thecapacitors 100-1 and 100-2 are inserted between the gate electrodes (G)of the first TFT's 32-1 and 32-2 and the common conductor 42 between thesecond TFT's 38-1 and 38-2 and the common TFT 41, even if the potentialdifference between the external output electrodes 16 and 18 and thecommon wirings 22 and 24 of the short ring 20 is reduced, continuitystate can be maintained still longer for a time required to charge anddischarge the capacitors 100-1 and 100-2, thereby further improving theefficiency of charge release. Also, by adding the capacitors 100-1 and100-2, the redundancy against defects due to shortage is improved. Sincethe electric charges are also released through a plurality of paths inthis embodiment, the redundancy as the electrostatic protection elementincreases in comparison with the case in the past having a single TFTand destruction of elements due to static electricity does not easilyoccur.

[0123] Next, the structure of the electrostatic protection circuitaccording to this embodiment is described with reference to FIG. 19.FIG. 19 shows a state of a single electrostatic protection circuit onthe substrate 1 on the array side when viewing toward the substrate. Thefirst distinctive characteristic of the structure shown in FIG. 19, withrespect to the structure shown in FIG. 15 is that the capacitors 100-1and 100-2 are formed by positioning the gate electrodes of the firstTFT's 32-1 and 32-2 at the lower layer of the conductor 42 via theinsulation film. Since other structures are the same as the structureshown in FIG. 15, description is omitted.

[0124] Next, an example of a variation of this embodiment is describedwith reference to FIG. 20 and FIG. 21. In order to reduce the number ofelements structuring the electrostatic protection circuits as many aspossible, the structure shown in FIG. 18 is further proceeded. Thestructures shown in FIGS. 20 and 21 have a distinctive characteristic inusing a single common TFT 41 among the electrostatic protection elementsections 28-1 through 28-n (or 30-1 through 30-n) of more than n (n isan integer of more than 3) bus lines. The distinctive characteristic ofthe circuit structure and element structure shown in FIGS. 20 and 21,with respect to the circuit structure and element structure shown inFIGS. 16 and 17, is that the capacitors 100-1 through 100-n are formedby positioning the gate electrodes of the first TFT's 32-1 through 32-nat the lower layer of the conductor 42 via the insulation film. Sinceother structures are the same as the structures shown in FIGS. 16 and17, description is omitted.

[0125] In the fabrication process of the TFT for the substrate 1 on thearray side where the electrostatic protection circuit according to thefirst through the seventh embodiments described above is formed, thequality of the panel may be judged by an open/short inspection (O/Sinspection), not by a TFT test, for simply detecting adisconnection/shortage of the bus line. In this case, in order to detectan interlayer shortage, the common wiring 22 of the short ring 20 on thegate bus line 2 side and the common wiring 24 on the data bus line 4side are required to be electrically separated by a high resistivecomponent. Accordingly, the structure shown in FIG. 22 can be taken asan example. In FIG. 22, for example, an interlayer separation portion 23having the similar structure to the electrostatic protection elementportions 28 and 30 described with reference to FIG. 2 through FIG. 11 inthe first through the fourth embodiments is formed at an intersection ofthe common wiring 22 and the common wiring 24.

[0126] Further, as shown in FIG. 22, by connecting either the commonwiring 22 or 24 (the common wirings 22 in FIG. 22) of the short ring 20to, for example, the common electrode 12 on the opposing substrate sideor to a connecting terminal 25 connected to ground, the TFT's and thebus lines can also be protected even more certainly from obstacles dueto static electricity.

[0127] Next, a liquid crystal display according to an eighth embodimentof the present invention is described. To begin with, a fabricationprocess of the substrate on the array side for a TFT-LCD used in thisembodiment is briefly described. First, a gate metal is deposited andpatterned on the substrate on the array side, and the gate bus line andthe gate electrode of the TFT in each pixel area are formed. Second, thegate insulation film is formed on the whole surface and an a-Si layer tobe an operating semiconductor film of the TFT and an insulation film forforming a channel protection film are deposited in this order on thegate insulation film. Third, by a back exposure using the bus line andthe gate electrode as a mask and an exposure using an ordinary mask toelectrically separate the a-Si layer from the pixel area, the aboveinsulation film is patterned and the channel protection film is formed.Fourth, an n⁺ layer to be an ohmic contact layer, the drain/sourceelectrodes and a drain metal (for example, Ti (titanium)) layer to formthe data bus line are formed in this order on the whole surface. Fifth,the n⁺ layer and the drain metal layer are patterned and thedrain/source electrodes and the data bus line are formed. Sixth, thepassivation film (for example, SiN film (silicon nitride film) is formedand then patterned, and a contact hole is formed at a predeterminedposition on the passivation film. Seventh, by depositing the ITO on thewhole surface and then patterning, the pixel electrode is formed. In theabove process, the exposure process is included in the first, third,fifth, sixth and seventh processes, resulting in a five-mask processusing five masks in total.

[0128] The electrostatic protection circuit of this liquid crystaldisplay formed including the above processes is described in detail withreference to FIGS. 23a through 27. It will be noted that, in thisembodiment, the structuring elements having the same function andoperation as in the first through the seventh embodiments are designatedby the same codes.

[0129]FIG. 23a shows a state of the substrate on the array side whenviewing toward the substrate. FIG. 23b shows a cross section cut at aline A-A′ in FIG. 23a. FIGS. 23a and 23 b show a state of the externaloutput electrode 18 pulled out of the data bus line 4 (not shown) on thesubstrate 1 which is a glass substrate on the array side and formed. Theelectrostatic protection element section 30 is formed at a tip of theexternal output electrode 18, and the external output electrode 18 andthe common wiring 24 of the short ring 20 are connected via theelectrostatic protection element section 30. Although omitted in thediagram, the structures of the gate bus line 2 and its external outputelectrode 16 are similar to the structures above.

[0130] As shown in FIG. 23b, the gate insulation film 52 according tothe second process above is formed on the substrate 1 on the array side.The drain metal layer according to the fourth process is patterned andthe external output electrode 18 and the common wiring 24 are formed onthe gate insulation film 52. Further, a metal layer 200 which patternsthe drain metal layer constructing a part of the electrostaticprotection element section 30 is formed on the opposite side of theexternal output electrode 18 and the common wiring 24. The passivationfilm 54 is embedded between both end portions of the opposing metallayer 200 and the end portions are electrically separated. Contact holes98 which open the passivation film 54 are respectively formed on bothend portions of the opposing metal layer 200. The ITO layer 43 which isa conductive film deposited in the seventh process is patterned on theinterior walls of the two contact holes and between the contact holes,and the two opposing metal layers 200 are electrically connected by theITO layer 43. In this case, the lower layer drain metal (Ti) and theupper layer metal (ITO) form an ohmic connection and a resistivecomponent varies depending on the size of the contact hole. When Ti isused for the lower layer metal, a heat treatment (for example,approximately 180° C. through 215° C.) is performed before depositingthe ITO and when the diameter of the contact hole 98 is φ=4 μm, theresistive component to be formed is 7 to 8 kΩ. Since the contact hole 98is formed in the sixth process above and the ITO film is also formed inthe seventh process, the electrostatic protection circuit can be formedwithout changing the conventional fabrication processes at all.

[0131]FIGS. 24a and 24 b show examples of variation of this embodimentwhich serially connects a plurality of contact holes 98 in order to makethe electrostatic protection element section 30 to have a high resist.In FIG. 24a, a plurality of island-like metal layers 202 are furtherformed between the two opposing metal layers 200 where the tips arearranged on the opposing sides of the external output electrode 18 andthe common wiring 24. The contact holes 98 are formed on the passivationfilm 54 on both end portions of the plurality of metal layers 202 linedup linearly. The adjacent metal layers 200 and 202 are electricallyconnected by the ITO layer 43 via the contact holes 98.

[0132] In the structure shown in FIG. 24b, electrically floatedisland-like metal layers 204 are arranged adjacent to each opposing endportion of the metal layers 200 and 202 lined up linearly, and thecontact holes 98 are formed on both end portions of the metal layers204. Each opposing end portion of the metal layers 200 and 202 isconnected at the connection layer of the ITO layer 43 via the metallayer 204 and the contact holes 98. By arranging the electrostaticprotection element section 30 in a zigzag line in this manner, thedistance between the common wiring 24 and the external output electrode18 can be reduced.

[0133] When reading the electric charges charged between the pixelelectrode and the common electrode by an array inspection device usingan integration circuit, the resistance value of more than 100 kΩ isdesired as an isolation resistance. Therefore, if the number of thecontact holes 98 are more than 14 by adopting the structure shown inFIGS. 24a and 24 b, the electrostatic protection circuit which does notaffect the array inspection can be realized. Thus, according to thisembodiment, the electrostatic protection circuit having an arbitraryvalue of resistive component can be formed by connecting a plurality ofsteps of the resistors via the contact holes.

[0134] Next, an example of a variation which makes the lower layer metalas a multi-layer structure in the electrostatic protection elementsection according to this embodiment is described with reference to FIG.25. FIG. 25 shows cross sections of the electrostatic protection elementsection in the formation process. A column (A) shows the gate bus lineside and a column (B) shows the data bus line side. Further, a row (a)through a row (e) show treatments in each process. First, in (a) of FIG.25, when the gate bus line and the gate electrode of the TFT are formedon the substrate 1 on the array side which is the glass substrate, ametal layer 200 g of the electrostatic protection element section 28 onthe gate bus line 2 side is simultaneously formed by gate metal. Whenforming the metal layer 200 g, the common wiring 22 of the short ring 20can also be simultaneously formed by gate metal. Next, the gateinsulation film 52 is formed on the whole surface by using, for example,SiN (silicon nitride).

[0135] Next, as shown in (b) of FIG. 25, when forming the data bus line4 and the drain/source electrodes of the TFT, a metal layer 200 d of theelectrostatic protection element section 30 on the data bus line 4 sideis simultaneously formed by using drain metal. The drain metal layer isconstructed by Ti/Al/Ti in order from the lower layer. Further, thecommon wiring 24 of the short ring 20 can also be formed by drain metalsimultaneously when forming the metal layer 200 d. Next, the passivationfilm 54 is formed on the whole surface.

[0136] Next, as shown in (c) of FIG. 25, the contact hole 98 is formedby opening the passivation film 54 on the metal layers on the metallayers 200 g and 200 d. Further, as shown in (d) of FIG. 25, the contacthole 98 where the upper portion of the metal layer 200 g exposes isformed by etching the gate insulation film 52 on the metal layer 200 g.In the process which collectively etches the passivation film 54 and thegate insulation film 52, the top drain metal layer, the Ti layer,functions as an etching stopper during the etching of the gateinsulation film 42. At this time, if the thickness of the top drainmetal layer Ti is thin, the underlying Al layer may be exposed.

[0137] Next, as shown in (e) of FIG. 25, the ITO layer 43 is formed bypatterning the ITO when forming the display electrode so that theadjacent metal layers 200, 202 and the like are electrically connectedvia the contact hole 98. At this time, since an ITO layer 43 a and theAl layer of the metal layer 200 d form a shot-key connection and thering-shaped Ti layer remained in the contact hole 98 and an ITO layer 43b form an ohmic connection, an overall contact resistance can beincreased. for example, when the drain metal is Ti(20 nm)/Al(75nm)/Ti(20 nm), the contact resistance per a contact hole on the metallayer 200 d is equal to 35 to 36 kΩ and if 3 or 4 of the metal layers200 d are serially connected, a state possible for the array inspectioncan be obtained.

[0138] It will be noted that by varying the temperature of the heattreatment under the condition that the metal layer is exposed at thebottom of the contact hole 98 and it is before forming the ITO layer 43,the contact resistance of the metal/ITO can be varied. When an elementhaving much higher resistance is required, the baking temperature may beincreased.

[0139] The resistance value of the resistive component formed in thismanner can be more than 10 MΩ. Even if the scanning signal, picturesignal or the like is applied to each bus line after the panel iscompleted, the adjacent bus lines can not be affected due to this highresistive component. Therefore, these high resistive components can beremained in the panel after the panel is completed. Thus, obstacles dueto static electricity in the unit assembly process after the panel iscompleted can be prevented, therefore the liquid crystal display can befabricated at a much higher yield and the reliability of the display canbe improved.

[0140] Although this embodiment described that the resistive componentswith the arbitrary resistance value can be arranged by lining up aplurality of the contact holes 98 linearly between each of the bus lines2 and 4 and the short ring 20 (the common wiring 22 and 24), thisembodiment is not limited to this and as shown in FIG. 26, the structureaccording to this embodiment can be formed between the adjacent gate buslines 2 or the adjacent data bus lines 4. In this case, theelectrostatic protection circuit can also be remained in the panel afterthe panel is completed by connecting the areas between the contact holesarranged on the metal layers 200, 202 and the like using the ITO layerand by forming sufficiently high resistive elements. The electrostaticprotection element portion according to this embodiment can certainly beformed without changing the fabrication process not only between theadjacent bus lines but also at an arbitrary position requiring the highresistive component.

[0141] Further, in the TFT fabrication process, the quality of the panelmay be judged by the open/short inspection (O/S inspection) for simplydetecting a disconnection/shortage of the bus line without the use ofthe array inspection. In this case, in order to detect an interlayershortage, the common wiring 22 of the short ring 20 on the gate bus line2 side and the common wiring 24 on the data bus line 4 side are requiredto be separated by the high resistive component. Accordingly, thestructure shown in FIG. 27 can be taken as an example. In the areaindicated by the dotted lines 120 in FIG. 27, a connecting state of thecommon wiring 22 of the short ring 20 and the common wiring 24 is shown.As shown in FIG. 27, by connecting a contact hole 121 where the endportion of the common wiring 22 formed by patterning the gate metallayer exposes and a contact hole 122 where the end portion of the commonwiring 22 formed by patterning the drain metal layer exposes by the ITOlayer 43, the high resistive portion can easily be formed at the endportion of connection. In the formation of the high resistive portion inthe contact hole 122, the resistance value can arbitrarily be adjustedby employing the method described in (d) and (e) of FIG. 25 above.

[0142] It should be noted that in the embodiment above, although thesilicon nitride film is used as the insulation film, a silicon oxidefilm (SiO₂ film) can certainly be used. Also, in the embodiment above,although the ITO is used for the connection layer between the contactholes 98, this embodiment is not limited to this and other materialsrelatively high in resistance value may certainly be used. Further,although the layered structure of Ti/Al/Ti is used as the drain metal,molybdenum (Mo), tungsten (W), tantalum (Ta) and their alloy, or theirnitride oxide can be used instead of Ti for the upper metal layer, andcopper (Cu), Al alloy, Cu alloy and the like can be used instead of Alfor the middle layer.

[0143] It should be noted that the each of the structures described inFIGS. 23 through 27 in the embodiment above can apply to the interlayerseparation portion 23 shown in FIG. 22.

[0144] As described above, according to this embodiment, since the highresistive component can easily be formed and still the resistance valuecan be controlled, the device destruction due to static electricity canbe prevented and the array inspection can be highly accurately performedas well. Further, since the destruction of static electricity in theunit assembly process can be dealt with after the panel is completed, anincrease in production volume owing to the improvement in fabricationyield and still highly reliable display can be provided.

[0145] As described above, according to the present invention, theliquid crystal display provided with the electrostatic protectioncircuit superior in redundancy can be realized. Further, according tothe present invention, the liquid crystal display provided with thesufficient protection function against static electricity in whichrelatively low voltage generates for a long period of time can berealized.

[0146] Furthermore, according to the present invention, the liquidcrystal display enabling to take measures against static electricityuntil the final stage of the substrate assembly process can be realized.Also, according to the present invention, the liquid crystal display inwhich the electrostatic protection element portion does not affect thesize of the panel can be realized. Further, according to the presentinvention, the liquid crystal display having the electrostaticprotection element section in which the element structure is simple andnot unfavorable in controlling the current can be realized.

What is claimed is:
 1. An active matrix type liquid crystal displaycomprising: a switching element formed for each of a plurality of pixelsdecided by a plurality of bus lines; a short ring connected to theplurality of bus lines; and an electrostatic protection element portionformed between each of the plurality of bus lines and the short ring;wherein the electrostatic protection element portion comprises a thinfilm transistor having a source or a drain electrode connected to thebus lines and the drain or the source electrode connected to the shortring, a conductive material connected to a gate electrode of the thinfilm transistor, a first resistor connected to the conductive materialfor connecting the gate electrode of the thin film transistor to the buslines, and a second resistor connected to the conductive-material forconnecting the gate electrode of the thin film transistor to the shortring.
 2. An active matrix type liquid crystal display as set forth inclaim 1 wherein the gate electrode of the thin film transistor isconnected to the conductive material via capacitor.
 3. An active matrixtype liquid crystal display as set forth in claim 1 wherein the secondresistor is a common resistor connecting the gate electrodes of theplurality of thin film transistor to the short ring.
 4. An active matrixtype liquid crystal display comprising: a switching element formed foreach of a plurality of pixels decided by a plurality of bus lines; andan electrostatic protection element portion formed between the adjacentbus lines; wherein the electrostatic protection element portioncomprises a thin film transistor having a source or a drain electrodeconnected to one of the adjacent bus lines and the drain or the sourceelectrode connected to the other of the bus lines, a conductive materialconnected to a gate electrode of the thin film transistor, a firstresistor connected to the conductive material for connecting the gateelectrode of the thin film transistor to one of the bus lines, a secondresistor connected to the conductive material for connecting the gateelectrode of the thin film transistor to the other of the bus lines. 5.An active matrix type liquid crystal display as set forth in claim 4wherein the gate electrode of the thin film transistor is connected tothe conductive material via capacitor.
 6. An active matrix type liquidcrystal display comprising: a switching element formed for each of aplurality of pixels decided by a plurality of bus lines; a short ringconnected to the plurality of bus lines; and an electrostatic protectionelement portion formed between each of the plurality of bus lines andthe short ring; wherein the electrostatic protection element portioncomprises a first thin film transistor having a source or a drainelectrode connected to the bus line and the drain or the sourceelectrode connected to the short ring, a conductive material connectedto a gate electrode of the first thin film transistor, a second thinfilm transistor having a source or a drain electrode connected to thebus line, the drain or the source electrode connected to the conductivematerial, and a gate electrode electrically floated, and a third thinfilm transistor having a source or a drain electrode connected to theshort ring, the drain or the source electrode connected to theconductive material, and a gate electrode electrically floated.
 7. Anactive matrix type liquid crystal display as set forth in claim 6wherein the gate electrode of the first transistor is connected to theconductive material via capacitor.
 8. An active matrix type liquidcrystal display as set forth in claim 6-wherein a channel length of atleast one of the second and the third thin film transistors is shorterthan a channel length of the first thin film transistor.
 9. An activematrix type liquid crystal display as set forth in claim 6 wherein thethird thin film transistor is a common transistor connecting the gateelectrodes of the plurality of the first thin film transistors to theshort ring.
 10. An active matrix type liquid crystal display comprising:a switching element formed for each of a plurality of pixels decided bya plurality of bus lines; and an electrostatic protection elementportion formed between the adjacent bus lines; wherein the electrostaticprotection element portion comprises a first thin film transistor havinga source or a drain electrode connected to one of the adjacent bus linesand the drain or the source electrode connected to the other of the buslines, a conductive material connected to a gate electrode of the firstthin film transistor, a second thin film transistor having a source or adrain electrode connected to one of the bus lines, the drain or thesource electrode connected to the conductive material, and a gateelectrode electrically floated, and a third thin film transistor havinga source or a drain electrode connected to the other of the bus lines,the drain or the source electrode connected to the conductive material,and a gate electrode electrically floated.
 11. An active matrix typeliquid crystal display as set forth in claim 10 wherein the gateelectrode of the first transistor is connected to the conductivematerial via capacitor.
 12. An active matrix type liquid crystal displayas set forth in claim 10 wherein a channel length of at least one of thesecond and the third thin film transistors is shorter than a channellength of the first thin film transistor.
 13. An active matrix typeliquid crystal display comprising: a switching element formed for eachof a plurality of pixels decided by a plurality of bus lines; a shortring connected to the plurality of bus lines; and an electrostaticprotection element portion formed between each of the plurality of buslines and the short ring; wherein the electrostatic protection elementportion comprises a plurality of metal layers, an insulating layerformed on the plurality of metal layers, a contact hole formed byopening the insulating layer on the plurality of metal layers, and aconnecting layer electrically connecting between the metal layers viathe contact hole.
 14. An active matrix type liquid crystal displaycomprising: a switching element formed for each of a plurality of pixelsdecided by a plurality of bus lines; and an electrostatic protectionelement portion formed between the adjacent bus lines; wherein theelectrostatic protection element portion comprises a plurality of metallayers, an insulating layer formed on the plurality of metal layers, acontact hole formed by opening the insulating layer on the plurality ofmetal layers, and a connecting layer electrically connecting between themetal layers via the contact hole.
 15. An active matrix type liquidcrystal display comprising: a switching element formed for each of aplurality of pixels decided by a plurality of data bus lines and gatebus lines; a first common wiring connected to the data bus lines; asecond common wiring connected to the gate bus lines; and anelectrostatic protection element portion formed between the first commonwiring and the second common wiring.
 16. An active matrix type liquidcrystal display as set forth in claim 15 wherein the electrostaticprotection element portion comprises a plurality of metal layers, aninsulating layer formed on the plurality of metal layers, a contact holeformed by opening the insulating layer on the plurality of metal layers,and a connecting layer electrically connecting between the metal layersvia the contact hole.